Portable clock-radio alarm system



p 12, 1961 A. w. HAYDON ETAL 2,999,928

PORTABLE CLOCK-RADIO ALARM SYSTEM Filed Sept. 2, 1959 2 Sheets-Sheet 1 [l0 1 22 '4 FIG.

Audio Input V Second Detector 8 AVG Circuit 20 29 {8 I7 i II I AVC [M INVENTORS. ARTHUR w. HAYDON BY HENRY T. WINCHEL ATTORNEYS l I @M, M,M M

AVC I l p 1961 A. w. HAYDON El'AL 2,999,928

PORTABLE CLOCK-RADIO ALARM SYSTEM 2 Sheets-Sheet 2 Filed Sept. 2, 1959 lNVENTORS ARTHUR W. HAYDON HENRY T. WINCHEL llllllllll lw l llllllllllllllllllllllllllll ||L United States Patent "6 2,999,928 PORTABLE CLOCK-RADIO ALARM SYSTEM Arthur W. Haydon, Milford, Conn., and Henry T.

Winchel, Culver City, Calif., assignors to Consolidated Electronics Industries Corp., New York, N.Y., a corporation of Delaware Filed Sept. 2, 1959, Ser. No. 837,679 1 Claim. (Cl. 250-20) This invention relates generally to clock radios and more particularly to improvements in alarms for clock radios.

In portable battery operated radios it is commercially and practically desirable that the set be able to operate for months and even years without requiring a change of batteries. The almost exclusive implementation of transistor components into portable radio circuits has made this goal of long-lived operation an actuality. In portable clock-radios, however, the problem of efiicient low current operation still exists. This is because the clock places an additional load upon the batteries and because conventional alarm signals generated by buzzers or the like require relatively large amounts of power to operate.

A portable clock-radio combination which requires very little current to operate has been disclosed in the copending application of Haydon et al., Serial No. 754,- 603, filed August 12, 1958. This device employs transistors throughout the radio circuitry and a clock having -very low current requirements. In addition, a novel electronic alarm circuit is provided therein which is adapted to produce an audible alarm signal through the speaker of the radio. It has been found that the generation .of this alarm signal requires approximately the same amount of current as would be used in the normal playing of the radio, and consequently provides a considerable saving over electro-mechanical buzzers or similar devices. In this system, the radio is turned on by the clock according to a predetermined clock setting, and after a few minutes of normal radio operation, the electronic alarm is energized by a clock controlled switch. In an alternate arrangement, the clock will turn the radio on for a few minutes to awaken the sleeper by the playing of the radio itself and the alarm circuit will not be energized. Unfortunately, in the latter instance, if no incoming signal is being received by the radio, no sound will come from the speaker. This might occur if the set were not tuned in properly, or if the selected broadcasting station were not transmitting, or if the signal were interrupted by metallic building structures or the like.

The present invention was developed as a result of the problem presented by the last mentioned eventualities. In its broader aspects, the invention contemplates certain additions to standard radio receiving circuits for detecting the absence of a transmitted signal from a broadcasting station. Although the invention is not to be so limited, an immediate application therefor is in the field of portable clock-radios where the invention -may be used to furnish an alarm when no transmitted be reproduced by and emitted from the radio speaker as an audible alarm signal. Means are provided for effectively grounding or blocking the positive feedback 'voltage when the voltage ordinarily developed by an incoming transmitted signal is present.

-' -One of the specific means employed to selectively Y.

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and automatically control the generation of positive feedback oscillations in an amplifier includes a diode which is connected in series with the feedback circuit. A voltage bias across the diode is provided by some means such as a battery and at the same time the anode is connected to a negative voltage output from the automatic volume control circuit. In the absence of an automatic volume control voltage, which would occur when an incoming transmitted signal is not being received, the positive feedback voltage will pass through the diode to the input of the first amplification stage and will cause the amplifier to oscillate at a frequency within the audio range. When an incoming transmitted signal is received, the negative automatic volume control voltage appearing at the anode of the diode will overcome the battery bias and will render the diode substantially non-conductive. Hence, Whenever an incoming signal is received, no positive feedback signals Will be permitted to flow through the diode to cause the audio amplifier to oscillate.

Another specific means provided by the invention which controls the development of a positive feedback oscillation in an audio amplifier, is the second detector diode of a superheterodyne circuit. This diode will be rendered conductive by the LF. voltage which should be present at the diode if the set is tuned properly, and a broadcasting signal is being received. The LP. voltage under these conditions will be maintained at a substantially constant level by the automatic volume control system, which is standard in sets of this type. The feedback voltage is connected through a resistor and capacitor from the audio amplifier output to the detector diode or alternately to the input of the audio amplifier. When a transmitted signal is received, the diode will effectively shunt or conduct the feedback voltage to ground. In the absence of a transmitted signal the diode will be substantially non-conducting and sufficient positive feedback voltage will be developed across the detector diode and fed into the amplifier to sustain oscillation. Therefore, in the absence of an incoming signal, the diode permits the feedback voltage to be developed across the amplifier input to develop an oscillation therein.

As a further aspect of the invention, certain novel switching arrangements have been provided for energizing the feedback components in a clock-radio combination. Other aspects of the invention will become more readily apparent after an examination of the following detailed description which should be read in conjunction with the accompanying drawings, in which:

FIG. 1 is a simplified schematic illustration including a portion of a typical vacuum tube superheterodyne A.M. radio circuit, incorporating the inventors novelv alarm circuit; and

FIG. 2 is a schematic circuit diagram similar to FIG. 1 wherein transistors have been substituted throughout for vacuum tubes; and

FIG. 3 is a schematic representation of a modification provided by the invention, wherein certain novel clockradio switching arrangements have been incorporated.

With reference to FIG. 1, one of the preferred forms which the invention may assume employing vacuum tubes has been illustrated. In this figure, an audio amplifier 10 having two stages of amplification 11 and 12 is adapted to amplify an audio frequency input in order to energize speaker 13. The voltage output from the plate of the final or second amplification stage tetrode 14 is tapped intermediate the plate and the primary of the speaker transformer to obtain an audio frequency feedback voltage therefrom. This voltage is series connected through capacitor 17 to the cathode of diode 18 Capacitor 17 will effectively block the DC. voltage present in. the circuit and will conduct only an audio frequency feedback voltage therethrough. A small D.C. voltage is provided by battery 8 to 'bias diode is across the diode and render it conductive to the feedback voltage. Hence, when the diode is conducting, the feedback voltage may be conducted therethrough,.and through the series connected capacitor to appear at the grid 21 of triode 22. Since an even number of amplification stages have been employed, the phase relationship of the feedback AC. voltage will be additive in the first stage triode, causing the amplifier to oscillate. These oscillations will cause an audible signal to be emitted from the speaker 13. a

A conventional automatic volume control, or AVC circuit has been indicated at 23. The function of the AVG is to act as an automatic proportioning system for maintaining a steady signal strength level of LF. voltage output regardless of the flucutating signal strengths of the radio frequency signals being received. This is accomplished by introducing a negative feedback gain control voltage from the second detector to control the LP. amplifier gain in accordance with incoming signal strength. Resistor 26 and capacitor 27 have been provided, which function as a conventional audio frequency filter, to develop in effect a slow changing DC. voltage output representative of average incoming signal strength. The AVC voltage will be present whenever the set is tuned in properly and an incoming signal is received. This voltage is connected in series with resistor 28 to anode 29 of diode 18 to Overcome the voltage bias of battery B. Diode 18 will thereby be rendered substantially nonconductive and the freedback voltage will be effectively blocked. It will be understood that the strength .of the AVG voltage, despite variations which permit it toperform its compensating functions, will be at high enough values to overcome the battery bias across the diode during all normal operating conditions. Of course, if incoming signal strength fades below a certain minimum or is entirely non-existent, no AVC voltage will be present and positive feedback through the diode will not be prevented. Thus the system will function automatically to prevent feedback oscillations from developing whenever the set is tuned to and receiving a transmitted signal above a certain minimum strength.

FIG. 2 illustrates the use of transistors in a circuit similar to that shown in FIG. 1. Since the various 'com- .ponents are equivalent and function substantially the same as the vacuum tube component describedin connection with FIG. 1, a detailed description of the circuit of FIG. 2 is not thought necessary and has therefore been omitted. It should be further understood that the circuits of FIG. 1 and 2 may be altered and different elec- 'tronic units substituted to achieve substantially the same effects. For example, it will be apparent that a triode or equivalent transistor may be substitutedvfor the diode 13 with but minor variations in circuitry. This unit can be biased alternately by an AVC voltage or by an independent voltage to render the unit automatically conducting or non-conducting to control the generation ofa feedback oscillation.

FIG. 3 illustrates schematically another of the preferred forms which thepresent invention may take. .Included in this figure are certain novel clock-radio switching arrangements for selectively energizing the positive feedback circuit incorporated therein for alarm purposes. As in the prior embodiment, a feedback voltage is obtained by a tap located intermediate the output of the 'final amplification stage transistor 31, of audio amplifier 30 and the primary 32 of the speaker transformer. This voltage output is fed through series connected resistance 33 and capacitor 34 and is connected intermediate the anode 35 of the second detector diode 36 and resistance 37. Alternately, an audio frequency feedback voltage unaccompanied by a DC. voltage may be taken from the secondary of the speaker transformer. In that event, capacitor 33 may be eliminated since its sole purpose is to block the DC. voltage present in the primary 31 of the speaker transformer. 'By virtue of the AVG circuit, 38, whenever a broadcast signal is being received properly, a substantially constant LF. voltage will be developed across diode 36 and will render this diode conductive. In this circumstance, the positive feedback voltage will be reduced to a minimum amount due to the unfavorable voltage division that takes place between resistor 33 and the diode 36, and hence the amplifier will not oscillate.

in the absence of an LP. voltage, the diode will be substantially non-conductive to alternate half cycles of the feedback voltage. -A maximum feedback voltage will thus be developed across diode 36 and volume control potentiometer 39 connected in parallel. Amplifier 30 will thereby be induced to oscillate at some natural-resonant frequency in the audio range. Oscillations so developed will be emitted from the speaker as an audible signal or alarm. This signal or alarm will be produced whenever there is no incoming signal received and as a consequence, an LP. voltageis lacking to render the diode 36 conductive.

in order to provide selective control over the generation of alarm signals, a manual master switch 40 has been provided which operates in conjunction with certain timed switch connections *under the control of :the clock 41. Master switch 49 is equipped with three-positions, oif, radio, and alarm. The OE and radio-positions are adapted to control the operation of the radio for its normal entertainment use without placing the radio under the control of the clock. A switch 42 .in the feedback circuit, has'therefore been ganged-mechanically with the master switch 40 to open the feedback circuit whenever the switch 40 is placed in the radio position. This prevents a feedback oscillation'from developing which would occur while :the radio is being-tuned from station to station.

When it is desired that the radio function as an alarm device, the switch 49 is placed in the alarm position.

This has the effect of closing switch 42 in the positive feedback circuit and also of establishing an electrical connection from the battery to a clock operated :switch 43. The clock in turn is adapted to complete this electrical connection at a prescribed time in order to energize the radio. A clock which may be advantageously employed for this purpose has been described in detail in the copending application of Haydon et al., filed August 12, 1958, which has heretofore been referred to. The clock described therein has been provided with novel printed circuits in .association with timing gears. Preset energization of the radio is provided by contact being established between the clock gear circuits and base or fixed contacts, through the agency of a wiper arm. In this arrangement, the radio will be energized for ,a few minutes, and as the clock gearing moves beyond the point of contact, theradio will be turned off automatically.

It will be readily understood therefore, that When'the radio has been turned on automatically by some clock actuated means as just described, the radio will operate in one of two ways. If the set is tuned properly and is receiving a modulated broadcast wave, the set will play normally, presumably to awaken the user. If no incoming wave is being received, the second detector diode will be substantially non-conductive to alternate half cycles of the feedback voltage and an oscillation will develop in the audio amplifier to produce an audible alarm signal from the speaker.

A further switching arrangementhas been illustrated in FIG. 3 which may be optionally included as a follow Conductor 46 is the voltage supply line for the radio and intermediate frequency portions of the set.

When the master switch 40 is in the on position, switch 44 will make contact with the battery B so that current will be conducted to the radio and intermediate frequency portions of the set for normal entertainment purposes. When switch 40 is placed in the alarm position, the electrical connection through switch 44 will be opened. However, switch 45 which is normally closed, will maintain an electrical connection from the battery B to conductor 46 until, after a prescribed period of time, the clock causes the switch to open. When this occurs, the radio and intermediate frequency stages will be deenergized and the effect will be the same as if a transmitted signal were not being received. Consequently, no I.F. voltage will appear at the second detector diode and the positive feedback voltage will be conducted to the grid of the first amplification stage of the audio amplifier, causing an oscillation to develop in the amplifier.

The follow-up alarm system just described will provide a positive feedback alarm signal which will follow the playing of the radio after the radio has been turned on automatically by the clock. The follow-up alarm is a further safeguard should an unmodulated carrier wave be received, which could conceivably occur in early morning hours, when a transmitting station is merely warming up. In this event, the sleeper would be awakened by the positive feedback signal actuated by the follow-up alarm system.

It should also be apparent that the automatic feedback controlling means provided in the embodiment of FIGS. 1 and 2 may be substituted for the circuit illustrated in FIG. 3. This would have the effect of requiring an additional diode, other than the second detector, to act as a valve for controlling feedback oscillation. However, a practical advantage resulting from such a substitution would be to place the feedback voltage beyond the control of potentiometer 39. In the embodiment of FIG. 3, the user must make sure that the sets volume control is not set at so low a volume that neither the normal playing sound or an alarm signal can be heard.

The present invention may also be incorporated within the circuitry of a conventional F.M. radio receiver as will be readily understood by those skilled in the art. In this form, a positive feedback circuit would be incorporated which would cause the audio amplifier to oscillate in substantially the same manner as described in connection with A.M. circuits. These and other modifications may be made without departing from the clear teachings of the invention, the scope of which is defined in the appended claim in which I claim:

A radio receiving system for automatically detecting the presence or absence of a transmitted signal and for performing an alarm function in response to the absence of a transmitted signal, comprising circuit means for detecting said signal, said circuit means including automatic volume control voltage producing circuit means for automatically maintaining the strength of said signal at a substantially constant level, feedback circuit means including part of the voltage output circuit of an amplification stage in said radio receiving system for introducing a voltage additively into a preceding amplification stage such that said voltage will cause an oscillation to develop in the amplification stages across which said voltage is maintained, means for controlling the passage of said feedback voltage to said preceding stage comprising a diode connected in series with said feedback means, a source of biasing voltage normally biasing said diode to conduct said feedback voltage to said preceding stage, circuit means connecting the automatic volume control voltage producing circuit means to said diode to apply a voltage in opposing relation to said biasing voltage, said automatic volume control voltage being of such magnitude in relation to said bias voltage as to condition said diode to be substantially non-conductive of the positive feedback voltage when a transmitted signal of minimum predetermined strength is being received.

References Cited in the file of this patent UNITED STATES PATENTS Kuhl et a1. Apr. 14, 1959 Blasbalg Aug. 18, 1959 OTHER REFERENCES 

